Milk shark

What it is

The milk shark is a member of the requiem shark family. It has a slender body with a long, pointed snout and large eyes. Its colour is plain grey or brown-grey on top and white underneath. Distinctive features include long furrows at the mouth corners and several enlarged pores nearby. It lacks spiracles behind the eyes. The first dorsal fin starts over the rear tips of the pectoral fins. This species is the largest in its genus, though most individuals remain under 1.1 metres in length.

Where it lives

This shark inhabits tropical coastal waters across the eastern Atlantic and Indo-Pacific. In the Atlantic, it ranges from Mauritania to Angola. In the Indian Ocean, it occurs from South Africa to the Arabian Peninsula and Southeast Asia. Pacific populations extend from China and Japan to northern Australia. It lives from the surface down to 200 metres depth. It favours turbid water near sandy beaches and often enters estuaries. Records exist of it swimming up rivers in Cambodia. Juveniles use seagrass meadows and tidal pools as nursery grounds.

How it lives

The milk shark is one of the most abundant near-shore sharks in its range. It feeds primarily on small benthic and bony fishes. Younger sharks eat more cephalopods and crustaceans, switching to fish as they grow. Predators include larger sharks like the blacktip shark and possibly marine mammals. Parasites such as the copepod Pseudopandarus australis affect this species. Evidence suggests males and females may segregate. Population numbers can fluctuate seasonally, with peaks in summer off South Africa.

Breeding and life cycle

Females are viviparous, sustaining embryos via a placental connection after initial yolk reliance. The reproductive cycle varies by region, occurring annually or less frequently. Litter sizes range from one to eight pups. Births happen in spring or summer in Africa, but year-round in Oman and Australia. Newborns measure between 32 and 50 centimetres. Females use warm inshore nursery areas for parturition. Males mature at smaller sizes than females, with variations across different geographic populations. The maximum lifespan is at least eight years.

Fish and people

Fisheries catch this shark using gillnets, trawls, and longlines. It is marketed fresh, dried, or salted for human consumption. The fins are used for soup, and the rest for fishmeal. It is a significant catch in countries like India, Senegal, and Oman. Some sport fishers target it. The common name stems from an Indian belief that its meat promotes lactation. Despite its abundance, heavy fishing pressure threatens populations. Earlier assessments of sustainable catches are now considered unreliable due to methodological flaws.

Status and threats

The International Union for Conservation of Nature lists the milk shark as vulnerable. While its reproductive rate allows some resilience, it cannot withstand high exploitation levels like some relatives. Fishing pressure has increased substantially in key regions since earlier studies. Stock assessments from the 1980s and 1990s suggested sustainable levels, but these methods were flawed. The decimation of larger shark predators by beach protection nets has led to local increases in milk shark numbers.

Relatives and look-alikes

It belongs to the genus Rhizoprionodon, which includes the Atlantic sharpnose shark. Phylogenetic analysis places it as the most basal of four examined species in this group. An extinct relative, R. fischeuri, from the Miocene epoch may be the same species. It is distinct from similar sharks by its mouth furrows and pore count. Confusion with other small coastal sharks is possible without examining these specific traits.

Questions people ask about Milk shark

Good reading and sources

• Milk shark on WikipediaEncyclopedia
• More photos on Wikimedia CommonsPhotos
• Wikidata recordOpen data